1. Field of the Invention
This invention pertains to a novel design for a collapsible hang glider, which is a glider type of aircraft having limited operator control, in which the point of novelty lies in the structure and arrangement of the airfoils and the capability to collapse the entire hang glider including folding the airfoils to a relatively small size for ease of transport.
2. Description of the Prior Art
Self-launched hang gliding began with the earliest pioneers of aviation during the late 1800's. Recently this method of aviation has undergone a rebirth of popularity. It has become a relatively low cost recreational activity spurred on by man's age old fascination with flight. Hang gliders may be flown anywhere that suitably sloped terrain faces prevailing winds.
Hang gliders in flight are governed by the same principles which affect all other flying machines. Lift and drag are prime considerations with respect to performance. Wing span, wing loading, and air speed are also important factors to be considered in the performance of the aircraft especially when maneuvering or turning the aircraft. Most hang gliders are launched by a running jump off a hill. The pilot controls the flight with body english. Most commercially available models provide a downhill ride of a few seconds or perhaps a brief soar along a ridge when the wind is right.
The Rogallo-type glider, the best known of hang glider models, is the ancestor of recent models. The main features of the Rogallo are a flexible delta wing, ease of assembly and disassembly and transport. When deployed, the shape of the glider is maintained in the shape of an inverted "V" by a tubular aluminum frame reinforced by a system of tension lines. Most commercially available models of the Rogallo-type have a sail area of approximately 208 square feet, a wing span of 24 feet, a glide ratio of 4:1, a stall speed of 14 MPH and a sink rate of 450 feet per minute. The Rogallo is relatively safe for a beginner to operate when properly instructed.
The leading edge of the sail is secured around a tubular frame to create the airfoil. The trailing edge should not be taut, but be able to reflex slightly; nor should this edge have tape sewn to it to make the edge semi-rigid. Making the sail more taut, which would tend to increase the glide ratio, decreases the craft's stability. Battens, which do make a sail more taut, are recommended only to correct a poorly contoured sail or to increase stability if high speed flight (35 MPH) is anticipated. Usually battens only add excess weight which in turn reduces overall performance of the Rogallo models.
More recent designs of hang gliders have attempted to achieve a craft with higher performance characteristics. With these high performance craft, hang glider pilots are looking toward flying under marginal conditions, toward achieving greater soaring feats and toward attempting longer cross-country flights. Therefore, a craft with greater lift capability, flatter glide angle, lower sink rate, and more complete control than earlier craft are being developed.
A glider developed upon the principles of the Rogallo is the Eagle III, with its predecessor being the Eagle II. The Eagles were developed to create a high performance craft which would allow continuous gliding on windward slopes with greater control and maneuverability. These models are considered to be easier to control in 180.degree. turns on windward slopes than the Rogallo models. Safety is another consideration of these models and was accomplished by designing a tubular leading edge of larger diameter than the Rogallo. This helps to create a deeper camber which in turn increases the lift and glide ratios. The result is a gentler stall and a descent which resembles that of a parachute-like descent.
The Eagle II is characterized by a non-swept sail wing. It has a sail area of only 150 square feet. The machine is comparatively heavy, weighing 75 pounds; thus, a critical aspect, that of wing loading, is a high coefficient, much greater than one. A loading coefficient of about one is optimum. High wing loading increases speed and sink rate but makes controlability easier, while low loading yields the opposite effects. The high wing loading is countered by the deep camber of the sail wing which improves lift, performance and stability. The lift coefficient of the Eagle II is about equal to two. These performance characteristics are similar to those of a large Rogallo model that is used to train beginners. This Rogallo model, however, because of its size, is not flown in winds much greater than 10 MPH as it is very hard to control and maneuver. When stalled, the Eagle-type glider tends to settle downward rapidly and nose down slowly, rather than abruptly go into a nose dive as the Rogallo-types are known to do.
The Eagle III is a high performance, monoplane type configuration with a variable camber wing. A tail is incorporated into the structure to give improved stability. The lift characteristics are similar to Eagle II but its weight is only 50 pounds. The Eagle III has a sail area of only 150 square feet but has an improved ratio of 10:1. The long wing creates slower and more sustained soaring flight but also creates problems when maneuvering. The longer the wing, the slower the wing tip moves during a turn which may result in spiral instability. The pilot is not able to easily control the craft by simply repositioning his body. Also the stall speed is relatively high, being 17 MPH, because of the small wing area; thus, this hang glider, because of its control problems, is recommended only for experienced pilots.
The monoplane and biplane configuration high performance hang gliders have a rigid construction making them difficult to transport. They have a large wing span and are prone to the same manueverability problems encountered by Eagle II and Eagle III. Rather than the pilot controlling the craft by shifting his weight, mechanical control mechanisms are necessary to maintain the craft's attitude. The major problem involves making the control system readily available to the pilot. Even when an efficient mechanical control system is devised, the amount of control is less than the full three-axis control of a Rogallo or Eagle-type glider.
Examples of these hang gliders are the Icarus V, XJ-24, and Swingwing. These have been developed, as has been the Eagle III, for high performance, sustained soaring flight. The glide ratio approaches 10:1. The weight of these craft ranges from 50 to 100 pounds. The stall speeds range from 16 to 19 MPH. These models are definitely not recommended for beginners.
The hang glider disclosed herein was designed to combine the advantageous characteristics of the previous hang glider models, which include: high performance, simple construction from lightweight materials, ease of assembly and disassembly, safety, easy portability and relatively low expense. The design maximizes lift, decreases drag, and improves stability.
The swept upper wing has a nonrigid leading edge which is not formed by aluminum tubing as in prior art hang-gliders. The leading edge is simply made of fabric reinforced with nylon fabric tape. Stranded cable is secured within the seamed edge to maintain structural integrity. The airfoil shape of the wing is achieved by a combination of, the binding in the fabric along the leading edge, the formed wing tips, the long batten positioned longitudinally along the center of the wing and the bridge member positioned between the sail and the forward keel member. The nonrigid structure of the wing produces a variable camber which in turn maximizes lift when flying at slow speeds.
A glide ratio of 9:1 is achieved even though the wing span is only 22 feet. This is accomplished due to the positioning of a novel lower undercambered sail wing below and rearward to the upper wing. The lower wing forms a large dihedral angle, which, in turn, forms a very efficient airfoil yielding added lift and stability. Due to the large sail area, the wing loading is approximately one-third less than that of the Rogallo types which enables slower flying speeds and a slower, softer rate of decent. The incorporation of the sail wing also creates greater maneuverability. Since the lower sail wing allows for a shorter wing span, spiral instability is reduced greatly.
A minimum of support structure is used. The frame simply consists of a two-member sectioned keel and two transverse frame members. The forward keel member and transverse frame members converge and attach to a collar which surrounds the leading apex of the after keel member. The frame is so assembled that it may be easily collapsed. A standard sized passenger type motor vehicle may be used to transport the collapsed hang glider.
The craft is extremely safe for beginners as it is easily controlled by body english. It naturally tends to return to level flight when put in a banking position rather than nose down and dive as the Rogallo types have a tendency to do. When stalled, the craft will act as a parachute. Descent may be made slowly and safely.
A Y-tail may be incorporated into the design to further increase stability. No additional mechanical controls are needed to operate this modification. The tail adaptation would be incorporated for high speed flying up to 40 MPH. It would also be used in erractic wind conditions and in cross-country flight by experienced pilots.